1. Field of the Invention
The present invention relates to metallocene-based catalyst precursors activated with cocatalysts comprising mixtures of at least two compounds, to the resulting catalyst compositions, and to the use thereof in a process of polymerizing and copolymerizing olefins.
2. Description of Related Art
It is known that metallocene complexes of certain transition metals, such as titanium, zirconium and hafnium, activated with aluminum compounds of the methylaluminoxane type, produce olefin polymers and copolymers, such as ethylene and propylene homopolymers, ethylene-butene and ethylene-hexene copolymers, e.g., see Kaminsky et al, U.S. Pat. No. 4,542,199 and Sinn et al, U.S. Pat. No. 4,404,344, the entire contents of both of which are incorporated herein by reference. Methylaluminoxane is commonly produced by reacting trimethylaluminum with water or with hydrated inorganic salts, such as CuSO.sub.4.5H.sub.2 O or Al.sub.2 (SO.sub.4).sub.3.15H.sub.2 O. Methylaluminoxane can be also generated in situ in polymerization reactors by adding to them trimethylaluminum and water or water-containing inorganic salts. However, although such combinations of metallocene-based catalysts and methylaluminoxane are very effective olefin polymerization catalysts, the methylaluminoxane cocatalysts are expensive and can be utilized efficiently only if the olefin polymerization reactions are carried out in aromatic solvents (usually in toluene) and thus do not lend themselves to gas phase reaction. Accordingly, a need exists in the art for alternative cocatalysts for metallocene-based catalysts.
Mixtures of certain alkylaluminum halides, such as Al(C.sub.2 H.sub.5).sub.2 Cl, and alkyldistannoxanes, such as [(C.sub.2 H.sub.5)3Sn].sub.2 O, in aromatic and aliphatic hydrocarbons activate cobalt complexes soluble in these solvents, such as cobalt diacetylacetonate and cobalt triacetylacetonate, in polymerization of butadiene and 1,3-pentadiene, e.g., see P. Racanelli and L. Porri, Italian Patent 745741 (1965).
It is the object of the present invention to provide a cocatalyst for metallocene-based olefin polymerization catalyst precursors, the said cocatalysts comprising mixtures of at least two compounds.
It is an object of the invention to provide a catalyst including a metallocene derivative which can be used in ethylene homopolymerization or copolymerization undertaken under gas phase conditions.